/Engine/Source/Editor/UnrealEd/Classes/Editor/UnrealEdEngine.h
Puts all of theAVolumeclasses into the passed in array and sorts them by class name.
static void GetSortedVolumeClasses ( [TArray](API\Runtime\Core\Containers\TArray)< [UClass](API\Runtime\CoreUObject\UObject\UClass) * > * VolumeClasses )